1. Field
The present inventive concepts relate to a frequency doubler, and more particularly a frequency doubler having a voltage controlled oscillator and an XOR gate.
2. Description of the Related Art
A phase locked loop (PLL) is typically used in various kinds of electronic circuits. In particular, the phase locked loop is important to a communication circuit. In a wireless communication system, a wireless device (e.g., a cellular phone) generally uses a clock signal in the case of a digital circuit, and uses an LO signal in the case of a transmitter and receiver circuit. The clock signal and the LO signal are generated by using a voltage-controlled oscillator (VCO) that mainly operates in the PLL.
The phase locked loop generally includes a phase frequency detector, a charge pump, a loop filter, a VCO, and an XOR gate. In general, the phase frequency detector, the charge pump, and the loop filter detect a phase error between a reference signal and a clock signal, which are obtained from the VCO, and generates a control signal Vctrl for the VCO. The control signal controls the frequency of the VCO so that the clock signal is synchronized with the reference signal. The XOR gate may receive a multi-phase signal to double the frequency of the VCO.